Pollen barrier

A physical obstacle that hinders the movement of pollen from a field of genetically modified (GM) crops to neighbouring non-GM crops is called a pollen barrier. Such barriers are erected with the aim of reducing the out-crossing of GM plants. In the European Union they may, for example, help keep the GM content of neighbouring non-GM fields below the threshold of 0.9 percent - allowing conventional farmers to sell their harvest as non-GM products.

Design of pollen barriers

Pollen barriers can be made of any species of hedge, tree or tall plantings which physically limit pollen movement. However, the most efficient pollen barriers are made of non-GM crops of the same species as the GM cultivation. This kind of pollen barrier is often called a "buffer strip" or "buffer zone", and is not only a physical hurdle but also obstructs GM pollen by producing its own competitive, GM-free pollen which also may fertilise the neighbouring GM-free fields. Consequently, however, crops in the buffer zone, although originally non-GM plants, also catch a lot of GM pollen, produce a lot of GM fruit and are considered a GM crop when harvested.

Pollen barriers versus isolation distances

According to recent research, a buffer zone is more efficient than isolation distances. A few rows of non-GM crops are equivalent to several metres of isolation distance. Detailed recommendations, however, exist only for maize at this time. Since co-existence has become a major topic in European agriculture, several research programmes – including Co-Extra and SIGMEA - have emerged to investigate pollen barriers as a tool for the co-existence of GM and non-GM crops.

In other regions, where GM crops have been planted for years without co-existence regulations, individual research projects are analysing the effective degree of mixing between GM and non-GM crops. However, most countries where GM plants have already been grown on a large scale are home to fields with large average sizes. Due partly to the longer average distances required for pollen travel, no specific co-existence measures or isolation distances may be needed to maintain admixture below the threshold. However, in regions such as Western and Southern Europe, average field sizes are much smaller and result in a higher admixture of GM and non-GM crops through pollen movement. Due to the limited space available on small fields, isolation distances may be inapplicable for co-existence. Pollen barriers, such as buffer strips, may be an appropriate alternative.

External links

* [http://www.coextra.eu Co-Extra - European research programme on co-existence]
* [http://sigmea.dyndns.org SIGMEA - European research programme on the biological safety of GM plants]